Trenchless tunneling methods that create a tunnel by excavating of the tunnel while concurrently pressing or "jacking" a tunnel casing or liner into the newly excavated tunnel are well known. The methods of pipe jacking, auger boring and microtunneling all use a hydraulic ram for pushing a series of tunnel liner sections end to end into the tunnel forming a tunnel lining behind a tunneling excavation. The typical pipe jacking site includes a pit which is dug to a depth to which a pipe or a tunnel liner will be placed under a section of ground. A set of equipment used in the pit will include a hydraulic ram, a soil hauling device for removing a quantity of soil from the tunnel excavation face, a excavation device, a backstop for the ram to push against and sufficient space to lower a section of the tunnel liner into place. Outside the pit, a second set of support equipment will typically include a crane for lowering sections of pipe or tunnel liner and lifting excavated soil from the pit, digging equipment, and a set of various support equipment. The crew will include personnel working inside the pit and on the ground surface. The typical crew size is five persons in the pit, tunnel and above ground.
The tunnel excavation may be performed by a human using hand labor, a combination of human hand labor assisted by machine excavation, or a fully automated tunnel boring machine (TBM). By excavating and lining the tunnel concurrently, a tunnel cave-in or other dangers of the tunnel's unsupported faces are reduced. The tunnel excavation diameter is typically cut slightly larger than the tunnel liner sections to minimize compression of tunnel sections as they are pressed down the tunnels length.
Various tunnel liner cross section geometries have been used. Tunnel liner cross-sections have ranged from a rectangular shape to a circular shape. The tunnel liner section ends must match or link into the end of another similar tunnel liner section. A principal requirement of the tunnel liner section design is its capacity to withstand compressive stress from the hydraulic ram which presses the tunnel liner section into the tunnel. Each section after being pressed into the tunnel is then forced deeper into the tunnel by the next section inserted by the hydraulic ram. As each section is pressed by the ram, the previously inserted sections extend deeper into the tunnel forming the full tunnel liner.
As the tunnel liner receives more tunnel sections, the friction between each tunnel section's exterior surfaces and the surrounding soil structure accumulates. This accumulated friction forces the hydraulic ram to increase the amount of force required to press each additional tunnel section into the tunnel. The material strength of the tunnel section and an upper pressing limit of the hydraulic system "jacking" the tunnel sections limit the amount of force that can be applied to the tunnel sections. Thus, a method of reducing the friction is required to increase the length of the tunnel past these friction limitations. A method of lubricating the tunnel sections, is used that injects a slurry containing a composition called bentonite around tunnel sections as they are pressed into the tunnel at the hydraulic ram. Other methods also inject bentonite into the tunnel sections farther down the tunnel as the bentonite is lost or absorbed by the ground. Bentonite is a water and clay composition containing a potassium, calcium, or sodium montmorrillonite clay that exhibits thixotropic properties. A thixotropic property is a substance which is a liquid when agitated and returns to a gel state after agitation ceases. Industry calculations have estimated that lubrication of tunnel sections increases the length of tunnel sections that are insertable in a single tunnel by a thousand times based on the load attributable to friction. In industry studies, it is surmised that a gel layer which is formed by injecting sufficient thixotropic material around the exterior of the tunnel section will cause the tunnel sections to become "buoyant" and float on this gel layer as they are pressed into the tunnel. Experimental data indicates that this floating condition keeps the hydraulic forces required to press additional tunnels sections at roughly a constant value in loose soil and gravel below the water table.
Bentonite pumping is currently done in stages; the bentonite is mixed in a grout mixing unit, the bentonite is formed into a slurry or grout which is then transferred to a pumping station which is hand linked to orifices or hand operated valves that are located at an entrance or mouth of the tunnel or at several tunnel sections within the tunnel length. The valves are turned on by personnel in the tunnel if the tunnel is sufficiently large to admit a human. The preparation, pumping and distribution of the bentonite is largely dispersed and separate from the tunneling operation and requires additional personnel to operate and maintain the lubrication of the tunnel sections. Some integration has occurred by combining the mixing and pumping of the bentonite in the Akkerman bentonite pump model EH-2250. The EH-2250 eliminates the separate above ground mixing and pumping units and delivers a consistent and uniform bentonite slurry to the delivery point. The other aspects of bentonite delivery still require separate manpower intensive operations and require a crew member on a pipe jacking crew to implement bentonite pumping. The crew member has tasks of filling the mixing reservoirs with water and dry bentonite, operating the mixers, operation of the distribution pumping system and operation of tunnel valves. Once the tunnel is finished, a worker must to enter the tunnel to remove the conduit from the tunnel liner and to plug the holes that the bentonite was pumped through. This bentonite lubrication technique is limited to human sized tunnels.
Therefore, there is a need to provide bentonite lubrication in a trenchless tunneling operation that reduces manpower requirements and is a safe and efficient manner and mode of bentonite distribution over the current methods. There is also a need to provide selectively dispensed bentonite in tunnels which are too small for human entry